aneesh draft final

7/31/2019 Aneesh Draft Final

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Dept of electrical and electronics Page 1

OPTIMAL DISTRIBUTION VOLTAGE CONTROL AND

CO-ORDINATION WITH DISTRIBUTED GENERATION

BY

ANEESH K G

E7 A 7706

Guided by,

Dr K Bijuna Kunju

Dept. of electrical and electronics


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ABSTRCT

Distributed generation is becoming a common practice nowadays because of its

utilization of natural energy, high reliability and low transmission losses. But since the

output power generated from natural energy, like wind power, photovoltaics etc. are

influenced by meteorological conditions, the voltage at each node becomes a problem.

Here in this work, the optimal control of distribution voltage with coordination of

distributed installations, such as the load ratio control transformer, step voltage

regulator (SVR), shunt capacitor, shunt reactor, and static var compensator are

presented. The communication infrastructure Is assumed to be widespread. In order to

confirm the validity of the proposed method simulations are done for a distributed

network with distributed generation.


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INTRODUCTION

The increasing demand of electrical energy cannot be supplied with theconventional energy sources like hydro, thermal and nuclear power plants with

centralized power generation. So some new and renewable energy sources such as

photovoltaic, wind mills etc. are connected with the existing power system at points

where they are available. This process by which the generation of power is

decentralized and is made near to the load centers is termed as distributed generation

(DG). A high stability ,clean energy system with less transmission loss can be

implemented using distributed generation. But since the natural power generation

sources are influenced by the climatic conditions, the voltage at each node becomes a

problem. So proper control methods should be adopted for the optimal control of the

distribution voltage.

Here, In this work the optimal control of the distribution system is

done with installations such as load ratio control transformer (LRT), static var

compensator (SVC), shunt reactor (ShR), shunt capacitor (SC), step voltage regulator

(SVR) etc. The co-ordinate control of each of the equipments makes the voltage

stability. A wide spread communication channel such as optical cable is necessary to

control all the equipments with coordination.


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WHAT IS DISTRIBUTED GENERATION?

GROUP OF GENERATORS CONNECTED TO VARIOUS POINTS OF THE POWER SYSTEM

The decentralization of the electricity generation near to the load centers

where natural and renewable sources of energy is available is termed as distributed

generation.

The advantages of DG are ,

Transmission losses are minimum. Clean and natural energy with high thermal efficiency. Close to demand. Reliability of services. Economical energy production. Less vulnerable to outages.

The problems with DG are,

Since the o/p of natural energy sources depends on meteorological conditions,distributed generators connected to the downstream may produce backward

flow. So uni-directional flow of power gets affected.

Co-generators are more expensive/watts.

As distributed generation increases , the voltage at each node becomes a

problem.


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OPTIMAL CONTROL OF VOLTAGE USING DISTRIBUTED INSTALLATIONS

Modern electric power utilities are facing many challenges due to over

increasing complexity in their operation and structure. One of the main problem is

voltage instability. The main cause of voltage instability is the inability to meet the exact

demand of REACTIVE power. The voltage at the consumer should be maintained within

the range. The co-ordinate operation of some distributed installations is used for the

optimal voltage control of DG.

The distribution installations includes,

o Load ratio control transformer

o Static var compensator

o Shunt capacitors

o Shunt reactors

o

Step voltage regulator


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LOAD RATIO CONTROL TRANSFORMER ( LVR )

The transformation ratio of LVR can be changed at the time of load.

Ratio control methods Equivalent model of LRT

Multi point selector switch along with some crank shaft and cam

arrangements causes it to slide on the tapings. The self end information such as voltage,

current are measured and is compared with the target value which is determined

beforehand. The transformer tap location is adjusted so that the voltage is maintained

at the desired level. But the problems like non uniformity of load distribution, reversed

power flow may cause deviations from operating standard voltage at other points such

as end portion, etc. These problems can be minimized using centralized control.

STEP VOLTAGE REGULATOR (SVR)

step voltage regulator is simply a step up or step down transformer which is

connected in distribution feeder lines. It provides increments or steps of voltage change.

It either oppose or aid their respective voltages.

step voltage transformer(boost) step voltage transformer(buck)
http://1.bp.blogspot.com/-Hfuu2RLws4Q/TbEe9TdN4UI/AAAAAAAAAG0/qTY7kQ8gI1o/s1600/Step-down+Autotransformer.jpghttp://4.bp.blogspot.com/-eZBfWXJ8LTs/TbEet1ihi2I/AAAAAAAAAGw/bRTmUrcOlU4/s1600/Step-up+Autotransformer.jpghttp://1.bp.blogspot.com/-Hfuu2RLws4Q/TbEe9TdN4UI/AAAAAAAAAG0/qTY7kQ8gI1o/s1600/Step-down+Autotransformer.jpghttp://4.bp.blogspot.com/-eZBfWXJ8LTs/TbEet1ihi2I/AAAAAAAAAGw/bRTmUrcOlU4/s1600/Step-up+Autotransformer.jpghttp://1.bp.blogspot.com/-Hfuu2RLws4Q/TbEe9TdN4UI/AAAAAAAAAG0/qTY7kQ8gI1o/s1600/Step-down+Autotransformer.jpghttp://4.bp.blogspot.com/-eZBfWXJ8LTs/TbEet1ihi2I/AAAAAAAAAGw/bRTmUrcOlU4/s1600/Step-up+Autotransformer.jpghttp://1.bp.blogspot.com/-Hfuu2RLws4Q/TbEe9TdN4UI/AAAAAAAAAG0/qTY7kQ8gI1o/s1600/Step-down+Autotransformer.jpghttp://4.bp.blogspot.com/-eZBfWXJ8LTs/TbEet1ihi2I/AAAAAAAAAGw/bRTmUrcOlU4/s1600/Step-up+Autotransformer.jpg


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For example, if the transformer has a turns ratio of 10:1 with 1000 V

applied in the primary, then, the secondary voltage will be 100 V. Adding or subtracting

by using the connection mentioned above - the output voltage would be 1100 V or 900

V, respectively. Thus, the transformer becomes an autotransformer with the capability

to boost (raise/step-up) or buck (lower/step-down) the system voltage by 10%. The self

end information such as current and voltage is calculated by the tap position of SVR.

This information is compared with the desired values and controls the tap location of

LRT to settle the voltage at a desired value.

SHUNT CAPACITANCE

A capacitor or a group of capacitors which are placed across the

electrical lines to provide a voltage increase or to improve the power factor of the

circuit. They are less expensive to install and maintain. A switchable shunt can be

disconnected from the circuit when conditions are satisfactory. The SC must be switched

on / off according to the system reactive power demand. The shunt capacitors supply

necessary VAR to the system, thereby increasing the voltage level. Also whenever

inductive load is connected to the transmission line, power factor lags because of

lagging load current. To compensate, a shunt capacitance is connected, which draws

current leading the voltage. The net result is improvement of power factor.


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The on/off time and switching is done through centralized control,

by comparing the self end information with the target value. Online SC control and co-

ordinate control of SC and LRT are the common practices

SHUNT REACTANCE

Shunt reactors are inductors connected across the power lines to

provide reduction in overvoltage and for power factor correction. These reactors

consume the VAR of the system. They are also used at the end of the transmission line

to compensate for the reactive power generated by line capacitance. In case of long

transmission lines unloaded the receiving end voltages often goes higher than the

sending end voltage. This effect is Ferranti effect. The shunt reactor consumes this

reactive power and reduces the voltage level. Also the leading power factor can be

avoided by the action of shunt reactance.

Equivalent diagram of transmission line with line inductance, line capacitance and shunt reactor (g)

STATIC VAR COMPENSATOR ( SVC )

SVC is equipment that compensate for reactive power at high speed by controlling the

current of a capacitor by the thyristor. SVC not only regulates the system voltage by

reactive power correction, but for power factor control also. These are used near to the

places where the loads are varying rapidly.


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If the power system is capacitive (leading), the SVC will use reactors

to consume VAR from the system, lowering the system voltage. And if it is inductive,

capacitor banks are automatically switched in, thus providing a higher system voltage. In

static system of VAR compensation, instead of mechanical switches controllable

switches called thyristors are used for high reliability. The thyristors are controlled by

signal from the control system via optical cables. The reliability can be increased by the

controlled switching of the capacitors also with thyristors (thyristor switched capacitor)


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SIMULATION

The result of simulation done to check the validity of the proposed project is

as follows..

Consider a residential distribution network as shown with a photovoltaic equipment at

node 33.

RESIDENTIAL DISTRIBUTION NETWORK

The load curve of residential area and capacity factor of photovoltaic generation varies

as shown.

Load curve of residential area capacity factor of photovoltaic generation


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The voltage profile at various nodes with different control strategies at time 12.00 is as

shown. The four different control strategies are, uncontrolled, tap control of a

transformer, the tap of a transformer and the tap of SC and ShR, the tap of transformer,

as well as the tap of SC and ShR and SVC control.

At time 12.00 the photovoltaic generation is maximum. With no control on

the installations the voltage variation is maximum. And with the co-ordinate and

centralised control of all the installations the voltage at each node can be maintained at

the desired value.


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CONCLUSIONS

To meet for the increasing demands of electricity, distributed generation should beEncouraged.

The main problem with distributed generation is the voltage instability.

Distributed installations such as Step voltage regulator, Load ratio transformer,Static VAR compensator, Shunt capacitor, Shunt reactor etc. are used for optimal

control of voltage.

Reliable central co-ordination of voltage regulation is done using optical fibercables.

The co-ordinate and centralized control of all the equipments provides desiredvoltage regulation.

REFERENCES

K. Kabemura, K. Yonekura, T. Tsukamoto, K. Hashimoto, and M.

Hara, Application of dispersed autonomous voltage control system to

a real high voltage distribution network, Elect. Eng. Jpn., vol. 146, no.

1, pp. 2736, 2004.

N. I. Santoso and O. T. Tan, Neural-net based real-time control of

capacitors installed on distribution systems, IEEE Trans. Power Del.,

vol. 5, no. 1, pp. 266273, Jan. 1990. J. C.Wang, H. D. Chiang, K. N. Miu, and G. Darling, Capacitor placement

and real time control in large-scale unbalanced distribution systems:

Loss reduction formula, problem formulation, solution methodology

and mathematical justification, IEEE Trans. Power Del., vol. 12,

no. 2, pp. 953958, Apr. 1997.

www.wikipedia.org

www.ieeeexplore.ieee.org

www.cleanenergyauthority.com

R. H. Liang and C. K. Cheng, Dispatch of main transformer ULTC

and capacitors in a distribution system, IEEE Trans. Power Del., vol.16, no. 4, pp. 625630, Oct. 2001.

R. H. Liang and Y. S.Wang, Fuzzy-based reactive power and voltage

control in a distribution system, IEEE Trans. Power Del., vol. 18, no.

2, pp. 610618, Apr. 2003.
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